Sayyiduna Abdullah (may Allah be pleased with him) said that the Truthful and Believed one (peace and blessings be upon him) said: "Indeed, each one of you remains in his mother's womb for 40 days, then he is a clinging clot for 40 days, then a lump of flesh for 40 days. Then Allah sends the angel and has the soul breathed into him. Then the command is given for four things: his provision, his deeds, his lifespan, and whether he is fortunate or wretched are to be written." By Allah, besides whom there is no god: "One of you does the deeds of the people of Hell until only an arm's length remains, then what is written (i.e. the decree) overtakes him, and his end comes while he is doing the deeds of the people of Paradise, because of which he enters Paradise. And one of you does the deeds of the people of Paradise until only an arm's length remains, then the decree overtakes him, and he does the deeds of the people of Hell and enters Hell."
So the Prophet (peace and blessings be upon him) informed that the whole of his creation, after forty days, becomes a clinging clot for forty days, and then the whole of it, after eighty days, becomes a lump of flesh for forty days. Whoever holds that a child can come from two (men) would have to allow that part of it is fluid and part of it a clot, or part a clot and part a lump of flesh, and that is contrary to the apparent meaning.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الدعوى والبينات / 21280